Genmab Reports 75% Response Rate for Experimental Colorectal Cancer Drug
Key Facts
On October 25, 2026, Genmab announced updated follow-up results from a Phase 2 study testing its experimental drug petosemtamab with chemotherapy in patients with metastatic colorectal cancer. The objective response rate, including confirmed and unconfirmed responses, was 75% in the first-line setting and 67% in the second-line setting. The rates were based on median follow-up of 5.9 months for first-line patients and 7.1 months for second-line patients. The data covered 79 patients who received the combination through May 15, 2026, including 45 in the first line and 34 in the second line. The results provide an early signal of treatment activity, while comparison with another treatment remains dependent on Phase 3 trials.
In the first-line group, the response rate was 81% among patients with left-sided tumors, the population targeted by one of the ongoing Phase 3 studies. Genmab said most responses that were unconfirmed in earlier analyses were confirmed with longer follow-up. The disease control rate was also 95% in the first line and 93% in the second line. At the data cutoff, 76% of first-line patients and 74% of second-line patients were still receiving treatment. These measures reflect different aspects of the study results, from response to patients remaining on treatment, within a limited follow-up period.
In the safety analysis, petosemtamab-related adverse events led to discontinuation in 2 of 42 patients who received the combination with mFOLFOX6, or 5%, and in 1 of 37 patients who received the combination with FOLFIRI, or 3%. The study recorded no treatment-emergent adverse events leading to death. Infusion-related reactions occurred in 48% of patients who received treatment with FOLFOX and 43% of those who received it with FOLFIRI. Grade 3 infusion-related reactions occurred in 3 of 42 patients in the FOLFOX group, or 7%, and 1 of 37 patients in the FOLFIRI group, or 3%. These results place tolerability measures alongside the response rates reported by the company.
The study is open-label and single-arm, and includes patients with left- or right-sided tumors, without RAS or BRAF mutations, who have not previously received anti-epidermal growth factor receptor treatment. Participants receive 1500 mg of petosemtamab every two weeks with FOLFOX or FOLFIRI. The drug is an experimental bispecific antibody that targets the epidermal growth factor receptor and leucine-rich repeat-containing G protein-coupled receptor 5. Researcher Ruth Vera said the response rates in both lines, as the data mature over time, “may point to a potential new treatment approach” for these patients. She added that options remain limited for some patients with metastatic disease after chemotherapy and targeted therapy.
Genmab says its petosemtamab program includes 4 Phase 3 trials, including two in first- and second-line metastatic colorectal cancer that are enrolling patients. The first-line LAGER-CRC 1 study compares petosemtamab with cetuximab, with chemotherapy given in both arms. The study targets patients with unresectable or metastatic left-sided tumors and no RAS or BRAF mutations. These trials are the next step in evaluating the results seen in Phase 2. Genmab estimated that an investor update would take place on Wednesday, October 28, at 5:00 p.m. Central European Time, corresponding to 12:00 p.m. Eastern Time.
As for the stock, market data showed Genmab closing at $43.79 on October 23, compared with a close of $40 on October 22. Both closes preceded the October 25 announcement of petosemtamab results, so they do not reflect trading after the results were published. The U.S. National Cancer Institute estimates that about 1.9 million new cases of colorectal cancer are recorded worldwide each year, ranking it as the third most commonly diagnosed cancer. This prevalence places the disease among the areas of therapeutic development pursued by the company, but Phase 2 data alone do not settle the drug’s efficacy compared with other treatments. Results from the ongoing Phase 3 trials remain the next step in its evaluation.